1. Field of the Invention
The present invention generally involves the centrifugal casting of molten metal. More specifically, the invention relates to an improvement in the casting of molten metal in a rotating mold wherein the molten metal is derived from an arc gap between a pair of opposing electrodes, at least one of which is formed of the metal to be cast.
2. Description of the Prior Art
It is known to cast metal, particularly the production of fine grain castings from prealloyed metals, wherein the metal to be cast is configured as at least one of a pair of opposing electrodes which, upon the application of electrical energy thereto, strike an arc therebetween to provide the heat necessary for melting the consumable electrode. The molten metal droplets developed at the arc gap are thereafter cast within a rotating mold.
The electrodes are conventionally each of a corresponding cylindrical configuration and supported for rotation relative to each other about a common longitudinal axis. The centrifugal force developed by the rotating mold causes the molten metal received therein to be solidified into the desired casting.
Casting systems of this type have typically been utilized for the production of fine grain castings which are intended for subsequent working so as to impart desired strength and other structural properties to the final product. The presence of a fine crystalline structure greatly facilitates subsequent working of the casting, such as through forging and related mechanical procedures. It is therefore the primary aim of these conventional systems to produce castings wherein the rate of solidification of the molten metal from its origination at the arc gap to its final destination in the mold is as rapid as possible in order to produce the desired fine grain structure.
However, these known systems have been characterized by certain disadvantages. For example, if a casting to be made is large in size, then the electrodes must also be correspondingly large in order to supply the quantity of metal required. However, a serious problem has heretofore existed in the fabrication and alignment of the electrodes in order to realize their uniform depletion during the casting process. Typically, large electrodes are of cylindrical configuration and formed by casting from the desired metal. It is difficult to cast a large electrode which is not out of round or bent. While these deformities can be corrected through machining, this correction procedure is costly and results in an undesirable amount of scrap metal. Since a stub must be welded to the electrode in order to conduct the current thereto, any welding inaccuracy also compounds the deformity problem, thereby rendering the alignment of the electrodes a very difficult problem to solve. If the longitudinal center lines of the electrodes are located by reference to the attachment surface of the stub, the ends of the electrodes will wobble when the electrodes are rotated. If the longitudinal center lines are located by reference to the electrode surfaces, the ends of the stubs will wobble. Because conventional electrode systems align the electrodes on the same longitudinal center line, the resulting wobble of the electrodes cause their nonuniform depletion, even if the electrodes are isolated relative to each other. Though these systems are generally capable of producing fine grain castings, it is this alignment problem which also precludes the production of a sound casting having a uniform structure throughout the casting. When the casting is large and the molten metal droplets have a large distance to travel from the electrode edge to the casting surface of the mold, this causes the metal droplets to accumulate and solidify in the mold in clustered form, thus resulting in an unsound cast product. This is because the droplets leaving the electrode are at their melting point and very little heat has to be extracted to cause rapid solidification.